/*
 * File     : FieldOffset.java
 * Created  : 11 Apr 2011
 *
 * Copyright © 2011 Matthew Wilson (mj. {my-surname} .uk {at} gmail.com)
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package com.googlecode.dni.type.structure;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * <p>
 *  Annotates a structure field to specify a byte-offset within the structure.
 * </p>
 * <p>
 *  <em>Use this annotation with care.</em>  It implies you know the exact
 *  specifics of the platform, compiler, and their chosen structure layout.
 * </p>
 * <p>
 *  A simple use of a specific offset is to simulate a C union.  For example:
 * </p>
 * <pre>
 * struct shape
 * {
 *   enum { CIRCLE, RECTANGLE } type;
 *   union
 *   {
 *     struct { int cx, cy, radius } circle;
 *     struct { int x, y, w, h } rectangle;
 *   } dimensions;
 * }
 *
 * &#64;Structure
 * interface Shape
 * {
 *   Type getType();
 *   void setType( Type type );
 *
 *   &#64;ByValue Dimensions getDimensions();
 *
 *   &#64;Structure
 *   interface Dimensions
 *   {
 *     &#64;FieldOffset( 0 ) &#64;ByValue Circle getCircle();
 *     &#64;FieldOffset( 0 ) &#64;ByValue Rectangle getRectangle();
 *
 *     &#64;Structure interface Circle { ... }
 *     &#64;Structure interface Rectangle { ... }
 *   }
 * }
 *
 * </pre>
 *
 * @author Matthew Wilson
 */
@Retention( RetentionPolicy.RUNTIME )
@Target( ElementType.METHOD )
@Documented
public @interface FieldOffset
{

    /**
     * <p>
     *  The byte-offset of the field within the structure.
     * </p>
     *
     * @return the byte-offset
     */
    int value();

}
